Method and composition for controlling lost circulation in well drilling operations



United States Patent Ofifice 2,812,161 Patented Nov. 5,1957

IVIETHOD AND COMPOSITION FOR CONTROL- LING LOST CIRCULATION IN WELLDRILL- ING, OPERATIONS Eldon J. Mayhew, Aztec, N. Mex.

No Drawing. ApplicationSepternber 14, 1954, Serial N0. 456,075

8 Claims. (Cl. 2551.8)

This invention relates to a method and composition for controlling lostcirculation in deep well drilling operations, i. e., for preventing orstopping losses of the circulated drilling fluid into strata openingsencountered in a well formation.

In the drilling of oil Wells, gas Wells, and the like, the process ofpumping a drilling fluid through the well hole to and from the bottom isreferred to as circulation. The maintenance of circulation of thedrilling fluid is essential to successful drilling by the rotary method.The drilling fluid or mud is supplied at the surface of the well inlarge earthern pits or metal tanks and is pumped from these into thebore hole through the drill pipe and the drill bit to the bottom of thehole. 'The mud returns to the surface between the drill pipe and thebore hole wall, bringing with it the drill cuttings. The circulation ofthe mud serves not only to carry the cuttings to the surface but also tocool and lubricate the drill bit, thus making possible the furthereffective penetration of the bit into deeper geological strata. l a

The formation in which the well is being drilled often contains cracks,fissures, cavities orstrata of high velocity. When the drill entersstrata containing such, crevices, the mud flows away through thecrevices to create the condition called lost circulation. Drillingcannot continue under conditions of lost circulation because thecuttings soon pile up around the bit and lock the bit and drill stem inthe hole. Severe cases of lost circulation may require completeabandonment of the Well or so increase the cost of drilling that thewell becomes uneconomical.

In conventional drilling operations, an aqueous bentonite drilling mudis used until a condition of lost circulation occurs, whereupon afilling material is mixed with the mud and carried by it into thecrevices to, seal of leaks in the formation. The filling materials knownto be useful for this purpose include cotton-and other,

textile fibers, cane fiber, ground corn cob s, mica, expanded perlite,synthetic resins, peat. moss, cottonseed hulls, ground walnut hulls,shredded cellophane, sawdust, ground feathers, and various combinationsof't-hese and other materials that can be suspended in the drillingfluid.

The use of each of theseknown materials, however, presents importantpractical problems or shortcomings,

and none of them has proved to be entirely satisfactory.

Many of them are compressible and occupy only a small fraction of theirnormal volume under the hydrostatic pressure in the well. Compressiblematerials are likely to fail under the pressure changes produced bydifferential pump pressures or by moving the drill stem into or out ofthe well hole. Many of the known materials are organic materials thattake up water or hydrate orare chemically decomposed under theconditions encountered in the formation, so that they soften and fail intime and make it necessary to add more material in order to recovercirculation; moreover, the reaction products of such organic materialsoften contaminate the mud and necessitate expensive chemicaltreatmentsof the mud. The solid organic materials used are difficult tokeep suspended in the drilling fluid, being of a higher specific gravitythan the fluid, While materials such as expanded perlite, though easilyto suspend, become compressed to a specific gravity higher than that ofthe fluid under the pressure in the bore hole. Furthermore, the commonlyused materials lack adhesive power and are insoluble, and they have beenknown to become lodged in the wall of the bore hole so as to obstruct orseal off a producing oil or gas zone, thus causing a costly or even acomplete loss of production.

The object of the present invention is to provide methods andcompositions which will overcome the disadvantages above mentioned andby the use of which losses of circulation can be prevented or stoppedmuch more effec-v tively than in the use of techniques heretofore known.

I have discovered that this object can be achieved by providinggilsonite in a suitable granular form and, whenever a condition of lostcirculation occurs in the course of well drilling operations, forcingthe granular solid gilsonite into leaking crevices in the wellformation.

Gilsonite is a naturally occurring solid hydrocarbon that has a brownishblack color, is soluble in hydrocarbon solvents and is mined in variousgrades having various degrees of toughness and elasticity and varioussoftening temperatures. All the common varieties are substantiallyincompressible and have a specific gravity sufliciently near to that ofwater that properly sized granules of the gilsonite can be readilysuspended in aqueous liquid carriers. p v

The gilsonite to be used in any particular case is selected from amongthe several available varieties so as to possess desired degrees oftoughness and elasticity and a desired softening temperature, and thenhis crushed and screened or otherwise preformed so as to obtain it inthe form of solid granules having various sizes and size distributionssuitable both for sealing the crevices occurring in the wellformationand for being easily placed and kept in suspension in anaqueous liquid carrier used to carry it into the bore hole and force itinto the crevices therein. In general, the gilsonite here used consistsnearly entirely of granulesof sizes retained on a mesh screen, not morethan about 10% of the particles being of any smaller size, and a majorproportion of the granules have sizes in the range of minus 4 to plus 50screen mesh. The coarsest particles present in the gilsonite-added to adrilling mud must be capable of passing through the mud pump used at theWell.

Having thus provided a suitable granular form of gilsonite, losses ofcirculation can be stopped pursuant hereto by simply mixing the granulesof gilsonite with a portion of the aqueous drilling mud usuallycirculated through the bore hole and pumping the resulting suspensioninto the hole so that the mud will carry the gilsonite granules to theleaking strata and force them into the crevices therein. aqueous cementslurry or even clear water can be used as the liquid carrier, instead ofthe usual drilling mud.

It is necessary, however, that the carrier be an aqueous 50 pounds perbarrel of the mixture or suspension. For

severe conditions, this concentration may be increased to as much as 100pounds per barrel.

In some cases of lost circulation the use of a liquid l carrier is notnecessary; for example, where circulation is lost by reason of cavitiesin the formation at a rela- If desired, a conventional tively'shallowdrilling level. In such cases, the granular gilsonite may be simplypoured into the bore hole in a loose or dry form and then forced intothe cavities and connecting cracks by subjecting it to hydraulicpressure from-a conventional drilling mud or other liquid pumped overit.

According to a further feature of this invention, I carry out thedescribed operations by the use of a selected variety of gilsonite thatsoftens at a temperature above the temperature of the well formation butis quite tough and pressure resistant at the temperature of theformation. The softening temperatures of different natural varieties ofgilsonite range from as low as about 75 F. to asv high as about 760 F.,while the melting temperatures range from about 118 F. up to about 800F. In general the varieties useful pursuant hereto are those whichsoften at temperatures between 170 and .610 F., and those most commonlyused-soften at temperatures between 300 and 350 F. v 7

According. to another feature of this invention, the granular gilsonitemay be applied by forcing it into the formation crevices while it is ina softened condition. Softened gilsonite granules will readily entervarious forms of cracks or crevices in the formation, and they adherewell to. the cavity surfaces. The softening of the granules can beeasily brought about by heating them. When the well formation itself hasa relatively high temperature, the gilsonite used can be selected sothat it will soften at the temperature of the formation; and suchgilsonite can be poured into the formation, held in place until itsoftens, and then forced into the crevices. In other cases, thegilsonite to be used is selected with a softening temperature notexceeding 212 F. and a suspension of this granular gilsonite in anaqueous liquid carrier, for example, in the usual bentonite drillingmud, is heated to the softening temperature of the gilsonite beforebeing introduced into the well formation.

When the gilsonite used issoftened by heating it, the temperature of theformation strata can be utilized to cool and harden it in situ after itis forced into the strata cavities, so as to restore its desiredtoughness and pressure resistance and give it a permanent sealingeffect.

The following tables illustrate the preferred particle size distributionof granular gilsonite used according to this invention under differentconditions of lost circulation:

A. Particle'size distribution of granular gilsonite preferably used inaverage crises of lost circulation in oil wells Dryysiex'ra AnalysisPercentages Retained by Weight U. 8. Screen No.

Maximum Minimum Typical B. Particle size distribution of granulargilsonite preferably used in severe cases 0') lost circulatibn'in oilwells C. Particle size distribution of granular gilsonite preferablyused in worst cases of lost circulation in oil wells Dry Sieve AnalysisPercentages Retained by Weight U. S. Screen N0.

Maximum Minimum Typical 4 (4,760 microns)- 35 10 20 8 (2,380 microus)-75 16 (1,190 microns) 95 EXAMPLE I While drilling a 6,000 foot test wellwith the use of a conventional bentonite drilling mud, several cavitiesand cracks were penetrated in the formation strata, and a complete lossof circulation occurred.- During a twoweek period all available types ofknown lost circulation materials were used in efforts to restorecirculation, and 9 cement blocks were set in the formation, butcirculation was not restored.

After the failure of those efforts, cubic feet of granular gilsonitehaving a melting point of 270 F. was mixed with about 400 barrels of theaqueous bentonite mud. The mixture was heated to about F., the softeningpoint of the gilsonite, by means of steam pipes in the mud pit. Themixture was then pumped into the zone of lost circulation and allowed tostand for 2 hours. The formation temperature was 58 P. which hardenedand set the gilsonite. Circulation was immediately and permanentlyrestored by these steps.

The granular gilsonite used in this example had a screen analysis of thetype indicated in Table C above.

EXAMPLE 11 While drilling at a depth of 9,200 feet circulation wasl'ost,-and efforts to restore it by the use of common materialswereunsuccessful. Granular gilsonite having a screen analysis of the typeindicated in Table C above was thenv mixed into the aqueous bentonitedrilling mud to a concentration of 22 pounds of the gilsonite per barrel(611 pounds) of the mud. AboutSO barrels of this mixture were pumpedinto the bore hole and allowed to stand for about 1V2 hours, until the.hydrostatic pressure of the materialhad forced the gilsonite granulesinto theformation cavities. The result was a permanent restoration ofcirculation. p q

The granular gilsonite used in this example had a softening temperatureofabout 200 F.

EXAMPLE III While drilling a'ta depth of 970 feet, a 5 foot cavity waspenetrated, and no fluid would stand in the bore hole. A total oflOO'cubic feet of granular gilsonite was poured into the open hole, andan aqueous bentonite mud of usual composition was pumped in :ontop ofthe gilsonite to weight it down and force it back into crackscommunicatingwith the cavity. By this procedure full circulationwasrestored, and no further loss of circulation occurred at the samelocation.

The gilsonite used according tothis example had a softening temperatureof 320 F. and a screen analysis of the type indicated in Table B above.

While I haveset forth numerous details in the foregoing description andexamples of this invention, it will be understood that the inventionmaybe practiced in various ways without limitation to such detailsexcept'as may be required by a fair construction of the appended claims.

1. In Well drilling operations in which a drilling fluid is circulatedwithin the drill hole, a method of overcoming loss of the fluid to earthformations through which the hole is drilled, comprising circulating asthe drilling fluid an aqueous drilling mud having suspended thereinsolid granules of gilsonite in the proportion of from 10 to 100 poundsof the gilsonite per barrel of the drilling mud.

2. The method of claim 1, wherein the gilsonite has a softeningtemperature between 170 and 610 Fahrenheit.

3. The method of claim 2, wherein the softening temperature of thegilsonite does not exceed 212 Fahrenheit.

4. The method of claim 1, wherein the granules of gilsonite are ofvarious sizes, with the major proportion ranging from minus 4 to plus 50screen mesh in size.

5. A well drilling fluid, comprising an aqueous drilling mud havingsuspended therein solid granules of gilsonite in the proportion of form10 to 100 pounds of the gilsonite per barrel of the drilling mud.

6. The well drilling fluid of claim 5, wherein the gilsonite has asoftening temperature between 160 and 610 Fahrenheit.

References Cited in the file of this patent UNITED STATES PATENTS1,327,268 Christians Jan. 6, 1920 2,573,690 Cardwell et al Nov. 6, 19512,597,085 Larsen May 20, 1952 2,634,098 Armentrout Apr. 7, 19532,683,690 Armentrout July 13, 1954 OTHER REFERENCES Abraham: Asphalts,fourth edition, 1938, published by 20 Van Nostrand, New York, pp. 227 to236.

1. IN WELL DRILLING OPERATIONS IN WHICH A DRILLING DUID IS CIRCULATEDWITHIN THE DRILL HOLE, A METHOD OF OVERCOMING LOSS OF THE FLUID TO EARTHFORMATION THROUGH WHICH THE HOLE IS DRILLED, COMPRISING CIRCULATING ASTHE DRILLING FLUID AN AQUEOUS DRILLING MUD HAVING SUSPENDED THEREINSOLID GRANULES OF GILSONITE IN THE PROPORTION OF FROM 10 TO 100 POUNDSOF THE GILSONITE PER BARREL OF THE DRILLING MUD.